I have a binary segmentation problem with highly imbalanced data such that there are almost 60 class zero samples for every class one sample. To address this issue, I coded a simple weighted binary cross entropy loss function in Keras with Tensorflow as the backend.
def weighted_bce(y_true, y_pred):
weights = (y_true * 59.) + 1.
bce = K.binary_crossentropy(y_true, y_pred)
weighted_bce = K.mean(bce * weights)
I wanted to ask if this implementation is correct because I am new to Keras/Tensorflow and the optimizer is having a hard time optimizing this. The loss goes from something like 1.5 to 0.4 and doesn't go down further. Normal binary cross entropy performs better if I train it for a long time to the point of over-fitting. Before anyone asks, I cannot use class_weight because I am training a fully convolutional network.